1. Field of the Invention
The present invention relates to a roll over determining method and particularly to a roll over determining method which determines whether or not a vehicle is going to roll over on the basis of the degree to which the vehicle rolls.
2. Description of the Related Art
The technology disclosed in Japanese Patent Application Laid-Open (JPA) 9-240399 is known as a technology for determining whether or not a vehicle is going to roll over.
As is shown in FIG. 8, in this technology a roll angle sensor detects that the vehicle is in a roll state. When the vehicle rolls with more than or equal to a predetermined roll rate and the roll angle thus exceeds an upper limit, an instruction is given from an input port 72 to a high-speed control valve 76 of a posture maintaining air bag device 74 (also called a side air bag device) to open the high-speed control valve 76. As a result, high-pressure air flows into the air bag body 78, the air bag body 78 expands, and the position of the passenger seated in the front passenger's seat is maintained. If, however, for example, the acceleration in the sideways direction is small, or the passenger is wearing their seat belt, or is not seated in the seat, then the posture maintaining airbag device 74 is placed in a non-operational state. It is also possible to set the operating conditions of the posture maintaining airbag device 74 from the roll rate and the roll angle.
However, in the aforementioned technology, the operating space of the posture maintaining airbag device 74 is determined using a determining map of the roll rate and the roll angle. Therefore, when a vehicle rolls over while the vehicle occupant is being swung towards the outer side of the vehicle in the transverse direction thereof by the sideways acceleration that is generated when a vehicle turns, this sideways acceleration is not included as an element for determining the operation of the posture maintaining airbag device 74. Accordingly, at the point when the posture maintaining airbag device 74 begins operating, the gap between the vehicle occupant and the side of the vehicle, in other words, the space for the airbag to expand into, has already become greatly lessened, with the result that, practically speaking, the detection can be said to have happened too late.